Is there any performance gain for setting object references in the editor vs init them in Start function?

Is there any performance gain for setting object references in the editor, compared to initializing them in Start function for that component? Would there be less computations be done when the object gets to be active? or is the same thing happening even if I set the values in the editor?

I think this is a case of "it makes so little difference that it's probably not even worth looking into".

Unless you're looking up 100's of references during the Start function, the act of looking up references is going to be completely dwarfed by the act of instantiating the object at all - even if there's nothing in its Start() function.

AFAIK Start() is not called more than once for any particular GameObject - that is, it's not called when a GameObject which has been disabled at runtime is re-enabled, so there's no effect at all in this regard if you're repeatedly disabling and enabling an object.

If you're instantiating a prefab repeatedly (rather than re-enabling an existing GO), then each new GameObject's Start() function will be called, however if performance here is a problem you are much better off removing the need to instantiate at all (perhaps by cycling through a pool of re-usable GameObjects) because again, the performance cost of instantiating a new GameObject is going to massively outweigh the performance cost of any reference lookups in its Start() function.